The Zalman ZM-F4 is not your typical 120mm cooling fan. The Zalman ZM-F4 is a 135mm multi-purpose fan that uses standard 120mm mounting holes. Using “Advanced Sleeve” bearing, the ZM-F4 fan from Zalman spins at 900 to 1300 RPM with a noise level of 18 to 26 dBA. Since the ZM-F4 uses 120mm mounting holes, it can be used in place of a 120mm fan, whether inside a chassis or as an active cooling solution for an aftermarket heatsink. For an even quieter operation, Zalman includes silicone mounting pins and an RC56 resistor with every ZM-F4 fan package."

FULL STORY @ HEATSINKSFANS(http://www.hitechlegion.com/reviews/cooling/heatsinksfans/9069-zalman-zm-f4-135mm-fan)